System of measuring image of pattern in scanning type euv mask

ABSTRACT

A system of measuring an image of a pattern in a scanning type EUV mask may include a high-power laser output unit including a flat mirror and a spherical mirror, which are used to focus a high-power femto-second laser on a gas cell; a coherent EUV light generating portion generating a coherent EUV light; a pin-hole, a graphene filter, and a zirconium (Zr) filter; a stage; an x-ray spherical mirror configured to focus a coherent EUV light; a zone-plate lens placed between the stage and the x-ray spherical mirror; an x-ray flat mirror placed between the zone-plate lens and the x-ray spherical mirror; an order sorting aperture (OSA) placed on the stage and configured to transmit only a first-order diffraction light of the focused coherent EUV light; and a detector portion placed on the stage.

BACKGROUND OF THE INVENTION

The present disclosure relates to a system of measuring an image of apattern in a scanning type extreme ultraviolet (EUV) mask, which is usedfor a process of manufacturing a semiconductor device, and inparticular, an EUV mask scanning microscope system which is used when afine pattern is formed by an EUV exposure process that is one ofsemiconductor manufacturing processes.

An EUV exposure apparatus, which is used to fabricate a semiconductordevice using an EUV light having a wavelength of 13.5 nm, is beingexploited for a semiconductor fabrication process. By using the EUVexposure apparatus, it may be possible to effectively reduce a linewidthof a pattern, because the wavelength of the EUV light is shorter than awavelength (e.g., 193 nm) of the Argon fluoride (ArF) light used in theconventional exposure apparatus.

In the EUV exposure apparatus using light of a short wavelength, an EUVmask is used as a photomask to form a fine pattern. The EUV mask mayhave a different structure from that in the conventional ArF exposureapparatus. For example, the EUV mask is changed from a transmissionstructure to a reflection structure and is provided to have an optimizedreflectance to an EUV light having a wavelength of 13.5 nm.

A yield in a wafer-level process is directly affected by a process ofinspecting and correcting a defect in patterns of the photomask, whichis one of processes of manufacturing the EUV mask. This is because thedefect on the photomask is copied to all of wafers fabricated using theEUV mask. A defect pattern, which is found by the mask inspectionprocess, may be corrected by the correction process. An exposure processusing a wafer exposure apparatus may be directly performed on a wafer,and then, a SEM inspection process may be performed to examine whetherthe correction is successful. However, this method requires a largeamount of cost and a long evaluation time, and thus, in the current maskmanufacturing process, a system, which has a microscope structure and isconfigured to measure an aerial image of a mask and to emulate anoptical system in a wafer exposure apparatus, is used tocost-effectively evaluate influence of a pattern on a wafer.

Thus, in order to overcome these technical difficulties in theconventional technology, it is necessary to develop a mask measuringsystem, which can reduce cost and time in a mask manufacturing process,can measure an aerial image without a complex optical system forillumination, and can reconstruct aerial images for various illuminatingconditions through a single measurement process.

PRIOR ART DOCUMENT Patent Document

(Patent Document 0001) KR 10-1811306

(Patent Document 0002) KR 10-0875569

SUMMARY

An embodiment of the inventive concept provides a high-performanceaerial image measuring system for an EUV mask.

An embodiment of the inventive concept provides an aerial imagemeasuring system, which is provided for an EUV mask, and to which atechnology associated with a high-performance EUV optic system isapplied.

An embodiment of the inventive concept provides an aerial imagemeasuring system, which is provided for an EUV mask and includes anoptical detector portion, which is provided as a part of a scanning-typemicroscope, and to which a sense array technology capable of perfectlyemulating an inclined illuminating system(s) in an exposure apparatus isapplied.

According to an embodiment of the inventive concept, a system ofmeasuring an image of a pattern in a scanning type EUV mask may includea high-power laser output unit including a flat mirror and a sphericalmirror, which are used to focus a high-power femto-second laser on a gascell; a coherent EUV light generating portion including the gas cell,which is used to generate a coherent EUV light from light output fromthe laser output unit; a pin-hole, a graphene filter, and a zirconium(Zr) filter configured to remove a high-power laser beam from thegenerated EUV light; a stage, on which a reflection-type EUV mask isplaced, and which is configured to move the reflection-type EUV mask ina direction of an x- or y-axis; an x-ray spherical mirror configured tofocus a coherent EUV light on a zone-plate lens and thereby to improveoptical efficiency; a zone-plate lens placed between the stage and thex-ray spherical mirror to focus a reflected portion of the coherent EUVlight on a region of the reflection-type EUV mask; an x-ray flat mirrorplaced between the zone-plate lens and the x-ray spherical mirror toguide and reflect a beam, which is focused by the x-ray sphericalmirror, to the zone-plate lens; an order sorting aperture (OSA) placedon the stage and configured to transmit only a first-order diffractionlight of the focused coherent EUV light; and a detector portion placedon the stage and composed of a sensor array, which is configured tosense an energy distribution of the coherent EUV light according to anangle of a reflected portion of the coherent EUV light, when thetransmitted first-order diffraction light, which is a portion of thefocused coherent EUV light, is reflected by the region of thereflection-type EUV mask.

In an embodiment, the pin-hole, the graphene filter, and the zirconium(Zr) filter are simultaneously applied between first optical system inthe high-power laser output unit and second first optical systemincluding the x-ray flat mirror and the x-ray spherical mirror to filteran x-ray light from light including a femto-second laser beam and thex-ray light. The first optical system is an IR optical system before thepin-hole, the graphene filter, and the zirconium (Zr) filter. The secondoptical system is an EUV optical system after the pin-hole, the graphenefilter, and the zirconium (Zr) filter.

in an embodiment, the pin-hole is a filter using a difference inemission angle between a femto-second laser and an x-ray light, thezirconium (Zr) filter is configured to use high selectivity between alaser light and an x-ray light, and the graphene filter is provided tohave a good thermal durability and thereby to reduce a thermal damageissue in a subsequent step.

In an embodiment, all of the zone-plate lens, the order sortingaperture, and the reflection-type EUV mask are disposed in a horizontalstructure, and the order sorting aperture is a pin-hole and is placedbetween the zone-plate lens and the EUV mask to transmit only thefirst-order diffraction light, among light focused on the EUV maskthrough the zone-plate lens.

Here, the order sorting aperture may be provided between the EUV maskand the detector portion, and in an embodiment, the order sortingaperture may not be provided between the EUV mask and the detectorportion.

In an embodiment, a distance between the order sorting aperture and thereflection-type EUV mask is configured to be smaller than ⅛ of adistance between the zone-plate lens and the reflection-type EUV maskand to reduce a noise component, except for a focusing component, to alevel smaller than 4%.

In addition, the zone-plate lens, which is used to focus the x-ray lighton a pattern region of the mask, may have a structure, in whichmolybdenum (Mo) and silicon (Si) layers are alternatingly stacked, and agrating structure constituting the zone-plate lens may have anelliptical shape and may allow for focusing in an incidence direction,without changing a direction of the incident beam to an inclineddirection.

Furthermore, the femto-second laser beam may be focused in a directionfrom right of the spherical minor to left of the spherical mirror, andan output x-ray light may be focused in a direction from left of thex-ray spherical mirror to right of the x-ray spherical mirror.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically illustrating a system of measuring animage of a pattern in a scanning type EUV mask, according to anembodiment of the inventive concept.

FIG. 2 is a diagram illustrating an example of a light-transmissionstructure in the system of measuring an image of a pattern in a scanningtype EUV mask, according to an embodiment of the inventive concept.

FIG. 3 is a diagram illustrating an example of a measurement targetportion in the system of measuring an image of a pattern in a scanningtype EUV mask, according to an embodiment of the inventive concept.

FIG. 4 is a diagram illustrating an example of an array detector portionin the system of measuring an image of a pattern in a scanning type EUVmask, according to an embodiment of the inventive concept.

FIG. 5 is a diagram illustrating an example, in which an x-ray sphericalmirror and an x-ray flat mirror are placed in a different order fromthat in FIG. 1 , according to another embodiment of the inventiveconcept.

FIG. 6 is a diagram illustrating an example of an image obtained by anarray detector portion according to an embodiment of the inventiveconcept.

FIG. 7 is a diagram illustrating an array detector portion according toan embodiment of the inventive concept.

DETAILED DESCRIPTION

Hereinafter, a system of measuring an image of a pattern in a scanningtype EUV mask according to an embodiment of the inventive concept willbe described in more detail with reference to the accompanying drawings.

According to an embodiment of the inventive concept, a system ofmeasuring an image of a pattern in a scanning type EUV mask may includea high-power laser output unit including a flat mirror and a sphericalmirror, which are used to focus a high-power femto-second laser on a gascell; a coherent EUV light generating portion including the gas cell,which is used to generate a coherent EUV light from light output fromthe laser output unit; a pin-hole, a graphene filter, and a zirconium(Zr) filter configured to remove a high-power laser beam from thegenerated EUV light; a stage, on which a reflection-type EUV mask isplaced, and which is configured to move the reflection-type EUV mask ina direction of an x- or y-axis; an x-ray spherical mirror configured tofocus a coherent EUV light on a zone-plate lens and thereby to improveoptical efficiency; a zone-plate lens placed between the stage and thex-ray spherical mirror to focus a reflected portion of the coherent EUVlight on a region of the reflection-type EUV mask; an x-ray flat mirrorplaced between the zone-plate lens and the x-ray spherical mirror toguide and reflect a beam, which is focused by the x-ray sphericalmirror, to the zone-plate lens; an order sorting aperture (OSA) placedon the stage and configured to transmit only a first-order diffractionlight of the focused coherent EUV light; and a detector portion placedon the stage and composed of a sensor array, which is configured tosense an energy distribution of the coherent EUV light according to anangle of a reflected portion of the coherent EUV light, when thetransmitted first-order diffraction light, which is a portion of thefocused coherent EUV light, is reflected by the region of thereflection-type EUV mask.

According to an embodiment of the inventive concept, an aerial imagedevice may include four portions; 1) a light generating portionincluding an Infrare(IR) source 1 and a gas cell 4 1 generating EUVlight in high efficiency, 2) an x-ray optical system portion (e.g., aflat mirror or a spherical mirror) delivering the generated x-ray lightand/or EUV light to a zone-plate lens 12 in high efficiency or with highoptical performance, 3) a hybrid stage portion including a coarse stage,which is used to find a position of an EUV mask 15 to be measured, and afine stage, which is used to perform a scanning operation for forming animage, and 4) an optical detector portion or a sensor array 17configured to perfectly emulate an inclined illuminating part of anexposure apparatus.

Thus, the EUV mask measuring device according to an embodiment of theinventive concept may be configured to improve a light generatingproperty and efficiency of an optical system, and in this case, it maybe possible to improve performance of an aerial image measuring system.By using an array detection method, it may be possible to realizedesired performance in the measurement, without a complex illuminationsystem for emulating an illuminating system of an exposure apparatus.

FIG. 1 is a diagram schematically illustrating a system of measuring animage of a pattern in a scanning type EUV mask, according to anembodiment of the inventive concept. In an EUV light generating portion,an x-ray light may be generated by focusing a femto-second laser on agas in a gas cell 4, i.e. a higher order harmonic generation, and inorder to prevent a chirping phenomenon, in which a pulse width isincreased when the femto-second laser passes through a material, aspherical mirror, instead of a lens, may be used to focus thefemto-second laser on the gas.

To remove other light excluding an x-ray light emitted from an exit ofthe gas cell 4 including a gas supplying line 5, a pin-hole 6 may beplaced after the gas cell 4 to transmit an x-ray having a small beamemission angle and to transmit only a central portion of a femto-secondlaser light whose emission angle is greater than that of the x-ray. Ifthe femto-second laser light passed through the pin-hole 6 is directlyincident into a zirconium filter 8, the zirconium filter 8 may bethermally damaged. Thus, a graphene layer (e.g., composed of onlycarbon) having a good thermal resistance property may be used to absorbmost of the femto-second laser light and to transmit the x-ray light. Aweak femto-second laser light passed through a graphene filter 7 maycause a noise in a highly-sensitive detection sensor, and thus, thezirconium filter may be used to completely remove the femto-second laserlight and to transmit the x-ray light at high transmission ratio.

FIG. 2 is a diagram illustrating an example of a light-transmissionstructure in the system of measuring an image of a pattern 14 in ascanning type EUV mask, according to an embodiment of the inventiveconcept.

In an EUV optic portion, a focusing x-ray spherical mirror 10 (or aspherical condenser mirror) may be used to reflect an x-ray light 9,from which a noise is removed, to a flat x-ray flat mirror 11 (or ax-ray flat mirror 11 may be used to reflect an x-ray light 9, from whicha noise is removed, to a x-ray spherical mirror 10 as in FIG. 5 ) and tofocus light, which is incident into the spherical focusing mirror 10 andhas an incident angle smaller than 3°, on a region of the zone-platelens 12. a x-ray flat mirror 11 may be used to reflect an x-ray light 9,from which a noise is removed, to a x-ray spherical mirror 10 and tofocus light,

Here, a size of the focused beam may be controlled by adjusting a radiusof the x-ray spherical mirror 10. For example, a diameter of the focusedbeam may be adjusted to have a value similar to a diameter of zone-platelens 12, and in this case, it may be possible to improve the beamefficiency of the zone-plate lens 12 and to optimize an amount of thex-ray.

Both of the spherical mirror 3, which is used to focus the femto-secondlaser on the gas cell 4, and the x-ray-purposed spherical mirror 10,which is used to focus the x-ray light on the zone-plate lens 12, may beconfigured such that an angle of light incident thereto has an anglesmaller than 3°, and this may make it possible to improve opticalefficiency of the x-ray light focused on the zone-plate lens 12.

In addition, positions of the flat minor, which is used to focus thehigh-power femto-second laser on the gas cell, and the spherical mirrormay be exchanged, and similarly, positions of the x-ray spherical minor,which is used to focus the coherent EUV light and to transmit the EUVbeam to the zone-plate lens, and the flat mirror may be exchanged.

Furthermore, to improve efficiency in the process of collecting light,the spherical minor 3 and the x-ray spherical minor 10 may be placed tohave an incident angle smaller than 3°, as described above.

FIG. 3 is a diagram illustrating an example of a measurement targetportion in the system of measuring an image of a pattern in a scanningtype EUV mask, according to an embodiment of the inventive concept.

The zone-plate lens 12 may be a grating pattern, which is realized usinga stacking structure of molybdenum (Mo) and silicon (Si), and may have agreatly improved diffraction efficiency for a first-order light,compared with a conventional zone-plate lens realized using gold (Au) ornickel (Ni).

If the conventional zone-plate lens of a circular pattern shape isinclined in an direction of an incident angle, it may be difficult toplace the conventional zone-plate lens, due to a focusing distance issueand the consequent mechanical issue. However, the zone-plate lens 12according to an embodiment of the inventive concept may be provided tohave an elliptic pattern shape, and in this case, the zone-plate lensmay be placed to be parallel to a mask surface. An order sortingaperture 13, which is used to focus the x-ray light on a mask patternand to remove a noise light, not the first-order diffraction light, maybe placed on a mask to be spaced apart from the mask by a distancesmaller than ⅛ of a focal length of the zone-plate lens 12 and to beparallel to the mask, and in this case, it may be possible to maintainan amount of a noise light caused by a flare to a level of 4% or lowerrelative to a signal.

The EUV mask 15 may be scanned in both of the x and y directions throughan operation of driving a fine stage and may be designed such thatsignals detected during the scanning operation are provided to a signalprocessing unit and an image thereof is reconstructed by an aerial imagedevice, and this may make it possible to measure an aerial image. Acoarse stage may be placed below the fine stage and may be configured tomove the mask to a position of a desired image on the mask. According toan embodiment of the inventive concept, a stage 16 may include the finestage and the coarse stage, and in this case, the stage 16 may be drivenwith an improved accuracy.

FIG. 4 is a diagram illustrating an example of an array detector portionin the system of measuring an image of a pattern 14 in a scanning typeEUV mask, according to an embodiment of the inventive concept.

A detector portion 17 for detecting the x-ray light may include adetector array, and in order to effectively emulate a structure of anilluminating part of an exposure apparatus, a sensor array in thedetector portion may be designed to have a radial structure or acheckerboard shape.

An aerial image, which is reconstructed through a process of measuringlight using one of devices in the detector array, may be controlled toobtain an image optimized by adjusting a gain value of each pixel, andthis will be described in more detail with reference to FIG. 8 . Inaddition, an illumination property of an oblique optical system may berepresented by sigma (σ)=(θ/NA). Here, θ may be an incident angle, andNA may be a numerical aperture. Thus, an inspection apparatus and anexposure apparatus may be configured to have the same illuminationproperty (i.e., sigma (σ)), and in this case, the result inspected bythe inspection apparatus may be used in the exposure apparatus as it is.

FIG. 5 is a diagram illustrating an example, in which the x-rayspherical mirror and the x-ray flat mirror are placed in a differentorder from that in FIG. 1 , according to another embodiment of theinventive concept. Even when, as shown in FIG. 5 , the positions of thex-ray spherical mirror and the x-ray flat mirror are exchanged, it maybe possible to realize a scanning system having the same performance. Inaddition, although not shown in the drawings, the IR flat mirror 2 andthe IR spherical mirror 3 may be placed at exchanged positions and maybe realized to have the same performance. Since this change in order ofthe mirrors is included in an embodiment of the inventive concept, itmay be within a scope of the present invention.

As illustrated in FIG. 6 , a detector portion of an array cell structuremay be used to reconstruct an image from signals of all cells, and inthe case where only dipole-shaped cells are used to reconstruct theimage, there may be an EUV mask pattern capable of improving a contrastproperty of a corresponding signal value. In this case, by exploitingonly the dipole cell, it may be possible to increase precision ofline-width roughness (LWR). That is, it may be possible to emulate anilluminating part that is optimized to a shape of a pattern.

Here, if a gain value of a dipole-shaped cell, which is placed at theoutside, is adjusted to 0, the image reconstruction may be achievedusing only the dipole-shaped cell, and this will be described in moredetail below.

FIG. 7 is a diagram illustrating an array detector portion according toan embodiment of the inventive concept. In the exposure apparatus, bychanging an intensity of light to an incident angle of a beam incidentinto a mask (sample), it may be possible to adjust resolution of animage, which is obtained through a beam reflected from the mask. Toincrease the resolution of an image projected on a wafer, an expensiveexposure apparatus may be manufactured to change an intensity of a beamincident into the mask (sample) depending on an incident angle in ahardware manner, but it is not easy to actually manufacture a maskinspection device, in which an intensity of the beam incident into themask (sample) is changed depending on an incident angle. Thus, in theinspection device, a gain value of each pixel in an array, which is usedto measure the shape of the beam reflected from the mask, may becontrolled to obtain an equivalent effect of changing the intensity oflight to an incident angle of the beam incident into the mask. Thecontrolling of the gain value of each pixel in the array may beequivalent to changing the intensity of light to the incident angle ofthe beam incident into the mask in a hardware manner, and thus, even inthe inspection device, it may be possible to obtain a clear image.

That is, an obtained light intensity I_s(i, j), which is calculated andobtained by the detector array, may be given to satisfy the followingequation 1, and in this case, the obtained light intensity may be usedto design an illuminating part of a wafer exposure apparatus.

I_s(i, j)=α(i, j)*I_o(i, j)   [Equation 1]

where i is an index in an x direction and is one of 1, 2, p−1, p, p+1, .. . , m, j is an index in a y direction and is one of 1, 2, q−1, q, q+1,. . . , n. In addition, I_o(p, q) is an intensity of light measured atcoordinates (p, q), α(p, q) is a pixel gain value at the coordinates (p,q), an obtained light intensity I_s(p, q) is a product of the intensityI_o(p,q) and the gain value α(p, q). In addition, gain values of pixelsmay be controlled such that all of them are the same or are differentfrom each other or some of them are the same or different from eachother, and by controlling the gain values of pixels in various manners,it may be possible to adjust a real value, which is obtained from thearray, to a desired value. By adjusting a gain value of each pixel inthe array in such a manner, it may be possible to realize a clear imageon an inspection device, to apply the result to an actual exposureapparatus, and thereby to effectively execute an inspection process.

According to the afore-described embodiment, by obtaining a high-qualityaerial image, it may be possible to previously evaluate whether a defecton an EUV mask is copied to a wafer in a wafer exposure apparatus andthereby to prevent a lot of wafer-level defects from being caused by adefect of a mask pattern. This may make it possible to increase a waferyield.

According to an embodiment of the inventive concept, it may be possibleto improve an optical property (e.g., aberration), optical efficiency,and performance of the aerial image measuring system, compared with theconventional aerial image measuring system. In addition, by using anarray detection manner, it may be possible to measure an aerial imagethat is technically the same as an aerial image by a complexillumination system for emulating an illuminating system of an exposureapparatus, even when the illumination system is not used. Furthermore,by performing the measurement process just one time, it may be possibleto reconstruct aerial images for various illuminating conditions.

Thus, by obtaining an aerial image through a high performancemeasurement process, it may be possible to previously evaluate whether adefect on an EUV mask is copied to a wafer in a wafer exposure apparatusand thereby to prevent a lot of wafer-level defects from being caused bya defect of a mask pattern. This may make it possible to increase awafer yield.

While example embodiments of the inventive concept have beenparticularly shown and described, it will be understood by one ofordinary skill in the art that variations in form and detail may be madetherein without departing from the spirit and scope of the attachedclaims.

What is claimed is:
 1. A system of measuring an image of a pattern in ascanning type extreme ultraviolet (EUV) mask, comprising: a high-powerlaser output unit comprising a flat mirror and a spherical mirror, whichare used to focus a high-power femto-second laser on a gas cell; acoherent EUV light generating portion comprising the gas cell, which isused to generate a coherent EUV light from light output from thehigh-power laser output unit; a pin-hole, a graphene filter, and azirconium (Zr) filter configured to remove a high-power laser beam fromthe coherent EUV light; a stage, on which a reflection-type EUV mask isplaced, and which is configured to move the reflection-type EUV mask ina direction of an x-axis or y-axis; an x-ray spherical mirror configuredto focus the coherent EUV light on a zone-plate lens and to improveoptical efficiency; a zone-plate lens placed between the stage and thex-ray spherical mirror to focus a reflected portion of the coherent EUVlight on a region of the reflection-type EUV mask; an x-ray flat mirrorplaced between the zone-plate lens and the x-ray spherical mirror toguide and reflect a beam, which is focused by the x-ray sphericalmirror, to the zone-plate lens; an order sorting aperture (OSA) placedon the stage and configured to transmit only a first-order diffractionlight of the focused coherent EUV light; and a detector portion placedon the stage and comprising a sensor array, which is configured to sensean energy distribution of the coherent EUV light according to an angleof the reflected portion of the coherent EUV light, when the transmittedfirst-order diffraction light, which is a portion of the focusedcoherent EUV light, is reflected by the region of the reflection-typeEUV mask.
 2. The system of claim 1, wherein the detector portioncomprises a detector array, an obtained light intensity I_s(i, j), whichis obtained by a calculation in the detector array, is given to satisfythe following equation,I_s(i, j)=α(i, j)*I_o(i, j) where i is an index in an x direction and isone of 1, 2, p−1, p, p+1, . . . , m, j is an index in a y direction andis one of 1, 2, q−1, q, q+1, . . . , n, I_o(p, q) is an intensity oflight measured at coordinates (p, q), α(p, q) is a pixel gain value atthe coordinates of (p, q), and wherein the obtained light intensityI_s(p, q), which is obtained by the detector array, is given by aproduct of the intensity of light I_o(p, q) and the pixel gain valueα(p, q), and the obtained light intensity is used to design anilluminating part of a wafer exposure apparatus.
 3. The system of claim1, wherein the pin-hole, the graphene filter, and the Zr filter aresimultaneously applied between first optical system in the high-powerlaser output unit and second first optical system including the x-rayflat mirror and the x-ray spherical mirror to filter an x-ray light fromlight including a femto-second laser beam and the x-ray light.
 4. Thesystem of claim 3, wherein the pin-hole is a filter using a differencein emission angle between a femto-second laser and an x-ray light, theZr filter is configured to use high selectivity between a laser lightand an x-ray light, and the graphene filter is provided to have a goodthermal durability and thereby to reduce a thermal damage issue in asubsequent step.
 5. The system of claim 1, wherein all of the zone-platelens, the order sorting aperture, and the reflection-type EUV mask aredisposed in a horizontal structure, the order sorting aperture is apin-hole and is placed between the zone-plate lens and the EUV mask totransmit only the first-order diffraction light, among light focused onthe EUV mask through the zone-plate lens, and a distance between theorder sorting aperture and the reflection-type EUV mask is configured tobe smaller than ⅛ of a distance between the zone-plate lens and thereflection-type EUV mask and to reduce a noise component, except for afocusing component, to a level smaller than 4%.